Modern concrete is a very durable construction material and, if properly proportioned and placed, will give very long service under normal conditions. Many concrete structures, however, were constructed using early concrete technology, and they have already provided well over 50 years of service under harsh conditions.
In any case, hardened concrete structures are subject to damages which may be a result of e.g. inappropriate manufacture or deterioration from weathering or other harsh conditions by mechanical, physical or chemical attack. Therefore, repair and/or sealing of concrete structures can be necessary to improve durability of the structures. Needs for repair and healing of concrete structures are becoming more important and in the future will be an important market, as long life cycles in construction have an increasing potential.
Apart from concrete repair materials based on mineral binder suitable for repair or restoration of damaged structures, there exist a range of other materials which are used for repairing and/or sealing of concrete structures.
For instance, pure colloidal silica can be used for repairing and sealing of hardened reinforced concrete structures. Effectiveness is, however, low.
Sika Ferrogard® products such as Sika Ferrogare-903+ from Sika Schweiz AG are used as a corrosion inhibiting product or invasive repair. These products penetrate into reinforced concrete and form a film around the reinforcement. A disadvantage of corrosion inhibiting products is the difficulty to assess effectiveness of the product. A disadvantage of invasive repair is generally high costs, and considerable time and resources are usually required. Access is sometimes difficult.
Examples for water resisting and crystalline waterproofing concrete admixtures are Sika WT-200® series, Sika Schweiz AG, which are crystalline admixtures for self-healing concrete resulting in crystalline-based self-healing, which react with portlandite (calcium hydroxide) to create water-insoluble crystals. Crystalline admixtures for waterproofing are also sold by Xypex Chemical Corp.
Other examples of agents which are used for repairing and/or sealing of concrete structures are Bacillus sphaericus, zinc sulfate, alumina-coated silica nanoparticles, blast furnace slag or fly ashes.
The materials used for repair and/or sealing are often rather expensive or exhibit low performance. Many approaches do not support self-healing processes. The application to the concrete material can be complicated and time consuming.
DE 102008061837 A1 relates to the preparation of a moulded article wherein an internal lining is formed of a grain mixture in which a binder is injected. A binder described is composed of cement, a micro-silica suspension, a nano-silica suspension, water and a plasticizer based on polycarboxylate ether.
US 2013/281577 A1 describes aqueous additive compositions for modifying cementitious compositions comprising colloidal nano-particles consisting of silica and polycarboxylate ether.
EP 2251376 A1 is concerned with aqueous polymer dispersions comprising, in a preferred embodiment, inter alia 5-15% by weight of a comb polymer, 10-30% by weight of fumed or colloidal silica and 30-70% by weight of water.
JP 2014-177394 A describes a repair method for concrete structures wherein a restoring material is applied to a place where a portion of concrete structure is removed, wherein the restoring material is a mortar composition comprising inter alia cement, fluidizing agent comprising polycarboxylic acid-based copolymer and amorphous silica fine powder.
DE 102006 049524 A1 relates to aqueous dispersions comprising precipitated silica or silicate and plasticizer such as polycarboxylate ether to increase early strength of cementitious preparations.